Hydrogen purification method



E. D. KLEMA -HY'JRGGFJI PURFICATION METHOD Filed may 24', 194e PatentedApr. 3, 1951 einen HYDROGEN PURIFICATION METHOD Ernest D. Klema, Salina,Kans., assigner to the United States of America, as represented by theUnited States Atomic Energy Commission Application May 24, 1948, SerialNo. 28,798

This invention relates to methods and means for furnishingr a continuousand constant source of puried hydrogen or of mixtures of hydrogen andinert gases. A

Pure hydrogen or a mixture of pure hydrogen and inert gases is desirablefor use in certain scientiic apparatus and instruments. For example,such gases are particularly important in ionization chambers andcounters used for the investigation of nuclear radiation and the like.For such uses it is desirable that these gases be free of all impuritieswhich capture electrons, such as oxygen, water vapor, or the halogengases. Hydrogen and inert gases such as argon, f

however, usually contain oxygen and Water vapor in very small amounts.lThe small 'amounts of oxygen or waterrvapor originally present orpicked up from the containers are harmless for most uses but they reducethe value of the gas or gases when it is necessary that the gases besubstantially free of electron' capturing impurities. impurities such'as oxygen or water Vapor are also undesirable for use in scienticinstruments such as ionization chambers, because in addition tocapturing electrons, they also change the collection time,

reduce the pulse height, increase the saturation voltage, and in somecases cause deterioration oi the instrument.

In the past the hydrogen or hydrogen rare gas mixtures have been puriedby the method described by H. H. Barschall and E. D. Klema on page 18 of63d Volume of the Physical Review (1943) This method consists of passingthe material to be purified over platinized asbestos and a desiccatingagent. Although somewhat effective this method is not convenient to useand is not completely satisfactory.

The object of this invention is to furnish an apparatus and a method forenciently and conveniently purifying hydrogen or mixtures of hydrogenand inert gases.

A further object of this invention is to furnish an apparatus and amethod for continuously and eiciently preparing' pure hydrogen ormixtures of hydrogen and inert gases free of water, oxygen, andhalogens.

Still further objects and advantages of this invention will be apparentfrom the following description and from the single figure which shows aschematic arrangement of a purifier used to furnish purified gas to anionization -chamber in accordance with the method of this invention.

The objects of this invention are achieved by the process whichcomprises passing the hydro- V3 Claims. (Cl. 'Z3-210) f gen or mixtureof hydrogen and .inert gases over a hydride of 'a lightmetal of thethird period of the class consisting of calcium and titanium.

The apparatus for accomplishing the objects comprises purifyingmaterial, means for holding the purifying material, means for heatingand purifying material, means for utilizing the purified gas, andconnecting means betweenl said purifying and saidutilizing means whichpermits circulation of the gas.

Morel particularly the process comprises circulating the gas in seriesthroughthe utilizing means and then over oneor more heated hydrides ofthird period light metals, particularly calcium hydride and titaniumhydride, and thenyback tothe utilizing means. g

-lllhe-calciuin hydride or -titanium hydride is especially eiieetive inremoving oxygen, wat-er vapor, halides, or hydrohalides. Typicalreactions thought to be involved are as follows:

The method and apparatus of this invention can best be illustrated by anembodiment which is presented in the single gure hereby made part ofthis specification. It is given for the purpose of illustration only andis not intended to be limiting on the spirit or scope of the invention.

Example I additional layers of tape are placed around the coil. Thepurifier 5 is quickly filled with the purifying material 9 which iscalcium hydride ground to pass a 4 mesh screen and to be held on an 8mesh screen. The filling must be done as rapidly as possible because thecalcium hydride oxidizes extremely rapidly in air, a chunk becomingoxide powder in about thirty minutes. The inlet connection ll and outletconnection l2 are l/ inch steel pipes centered respectively about 1.5centimeters from the bottom and top of the puriner 5. A three-way inletvalve i3, and a three-way outlet valve lll are connected respectively inthe inlet connection H and outlet connection l2. The inlet and outletconnections l and l2 "are connected to glass tubing. i6 by joints whichare not shown. The ionization chamber generically indicated by I1 inwhich the purified hydrogen and inert gas or gases are to be used isconnected in series with the purifier 5 by means of glass tubing I6 andtwo joints which are not shown. The chamber il is a 3-inch hermeticallysealed metallic cylinder I8 containing a 25 mil diameter center wire i9.The center wire i9 'is anchored at one end by an electricallynon-conducting gas tight seal and at the other end by a similar sealthrough which it enters a coaxial cable and thus through the groundedshield 22' to a discriminator, such as the Schmitts-trigger varietywhich is not shown. The metallic cylinder i8 is connected to thepositive terminal of a high voltage direct current supply 23vwhosenegative side is grounded. A high resistance 24 is `placed between thecylinder i8 and the high voltage supply 23, and a condenser 2G is placedbetween the cylinder i8 and the shield 22 in order 4 to filter the highvoltage supply. A thin foil of radio-active material 2i, which emitsabout 5000 alpha particles per minute, is placed within the A cylinderi8. against its outer Wall.

In order to operate the apparatus, argon or nitrogen is first admittedinto the purier 5 by means of the inlet valve 13, and is allowed toexhaust through the outlet valve i4 until all the dust is removed fromthe purifying material 9. The heating coil I is then turned on, thesystem is evacuated by means of gas outlet valve i4 and the purifier 5is outgassed at about 250 C. Three atmospheres of 99.6 per cent argonand one atmosphere of substantially pure hydrogen are then introduced bymeans of the inlet valve i3 into the system. The temperature of thepurier 5 is tial between purifier 5 and chamber i1 causes the gas tocirculate between them.`

Potential of 540 volts is applied across the 3 .chamber and the biascurve is determined. Bias ""'curves are determined when potentials oi1025,

purities for a long period of time. For instance,

when the apparatus described in Example I is operated continuously for athree-day period, the v bias curve determinations at the end of thisperiod are identical with those originally-obtained under the sameconditions. When the gas is not purified the response is notconstantwith time, and the saturation voltage and pulse height decreasesdue to the changing purity of the gas mixture.

It is often desirable that a much smaller amount of hydrogen be used inionization chambers than the 25 per cent by volume of hydrogen used inExample I. Example II presents the pre- .ferred embodiment for suchcases in which 4the only hydrogen present is introduced by the hydrideused.

Example II The puriier 5 as used in Example I is filled with a mixturecontaining calcium hydride and a small amount of calcium which have bothbeen ground until they will pass a 4 mesh and be held on an 8 meshscreen. The system is assembled, evacuated, and 35 pounds pressure ofargon is then admitted. The purifier' is allowed to stand overnight at360 C. It is then operated at this tiplication is no longer occurringand that the purity of the gas is remaining constant.

The temperature is held in the range of L" C. to 525 C. and the biascurve is determined for potentials of 1025,. 2260, and 2975 volts. Allthree bias curves are nearly identical, thus indicating that saturationis obtained at or below 1025 volts.

Embodiments such as the onepresented in ExampleIl' have the advantage`thatreproducible, but very small amounts of hydrogen may be introducedand purified. It may be noted that in Example II, where only a smallamount of hydrogen was present, saturation was obtained at l a muchlower potential-than in the case of Example I w-here 25'per centhydrogen was present. The amount of hydrogen present may be increased byincreasing the temperature of the calcium hydride. It is interesting tonote that although the amount of hydrogen used in the ionization chamberil maybe reduced to a very small amount, it cannot be completelyeliminated because in itsabsence it is difficult or impossibletoobtainsaturation of the chamber Il. Apparently when the eld strengthnear the wall of the cylinder i8 is still too low to saturate thealphaparticle ionization, the eld strength near the 'wirel'iais-already.high enoughto cause multipli.

cation.

Other 'hydrides such as titanium hydride may beused as the purifyingagent. This is illustrated in Example III where the puried mixture ofgas is used in an ionization chamber similar to the one used in ExamplesI and II.

Example III,

The purifier 5 is filled vwith titanium hydride. 'Ihe system isevacuated and outgassed at 250D C.

One atmosphere of hydrogen and 3 atmospheres temperature, ora higherhydrogen pressure at the same temperature.

As inthe case of calcium hydride, it is possible to use titanium hydrideto purify substantially pure hydrogen or varying compositions ofhydrogen and inert gases.

It is to be understood that although the examples described thepurication of hydrogen "and argon used in an ionization chamber, the

same method and apparatus may be used for purifying hydrogen o r amixture 'ofvhydrogell and inert gases in any place where such a 28S ormixture of gases are needed. The method and apparatus will remove anyoxygen, water vapor, halides or hydrohalides which are present. As

S i. pointed out hereinbefore, in any such embodiment the compositionmay vary from substantially pure hydrogen containing no inert gas to thedetection or measurement of the properties of neutrons. For example,uranium 235 may be conveniently used as a neutron sensitive foil.

There are of course many variations of this invention. For example, therate oi circulation of the gas may be increased by introducing acirculating pump. -Ba'ilies may he "inserted inthe Y outlet of thepurier to prevent any dust from being circulated. Thesize and shape ofthe various parts of the apparatus may of course be varied. Thepurifying materials need not be ground to pass a 4 mesh screen and beheld on an 8 mesh screen, but may be of any size which presents suicientsurface area to carry out the purication of the gas in an efficientmanner.

Because of the many possible variations, it is to be understood thatthis invention is not to be limited in spirit or scope except asindicated in the appended claims.

What is claimed is:

1. A method of continuously removing oxygen,

water vapor, hydrohalides and halogens from a gas containing hydrogenwhich comprises passing the gas over a hydride of a third period lightmetal of the class consisting oi calcium and tita 5 nium heated to atemperature of at least 2o C.

2. A method for purifying gases containing hydrogen which comprisespassing the gas over calcium hydride which is maintained at atemperature of about 500 C.

l0 3. A method for purifying gases containing hydrogen which comprisespassing the gas over ti- Number Number tanum hydride which is maintainedatv atern.- perature of about 250 C.

ERNEST D. KLEMA.

REFERENCES CITED The Vfollowing references are of record in the l'e 'of'this "patent:

UNITED STATES PATENTS l Name Date Jost' Aug. 21, 1928 Freya 1 Apr. 17,1934 Marx May 19, 1936 Ramseyer Apr. 30, 1946 FOREIGN( PATENTS Country fDate Great Britain July2. 1908

